How can I create a snapshot of a curve in the Graph Editor (like Buffer Curve Snapshot feature in Maya)?
Yes it is called Create Ghost Curves

It will create a snapshot in dotted lines of the selected curve(s). That lime can then be used as reference. 

For 2.8 Use the icon at the top of the curve editor.


To clear the ghost curve it just click on the X icon again on the same place where you created the curve.

For older versions of blender select the curve, press the space bar to acces the search menu and type ghost curves. Then you can enable or disable the function.